I prefer Missy-G strap-on compared to other strap-ons I have used in the past. I use mine with the Goddess dildo which has a bullet vibrator that attaches to the dildo. I find this combination the best compared to the strap-ons with a pouch.

You might need to play around with positioning as well. Many harnesses ride up on the pubic bone when tight, but for best stimulation you want something that rides lower so it's over your clit and vulva.

Another option is the Aslan Double-Up Cuff. It allows you to mount a toy for you on your harness, either vibrating or not.